I have to agree with Stas. While the standard errors from
subsetting and from using -subpop()- might be indistinguishable, it
is not a given. My example was simplistic: there were no strata, and
clusters were independent of the subpopulation, weight, and analysis variables.

Another, potentially more serious, problem for subpopulation
analysis is not, I believe, mentioned in the SJ article: bias can
arise if the supplied weights, appropriate for the whole sample, are
wrong for the subpopulation. Levy & Lemeshow (2008, p.148) give a
simple example.

Thanks to both you and Stas. Just so I am clear, would this be a
problem even if using the subpop option, or only if using an extract?